1. Field of the Invention
This invention pertains to terrain elevation databases as applied in the field of avionics. The embodiments herein contain a system and methods for combining a plurality of terrain elevation databases having varying resolutions and parameters into a single database of a common resolution.
2. Description of the Related Art
Beginning in the early 1970's, a number of studies looked at the occurrence of “controlled flight into terrain” (CFIT)-type accidents, where a properly functioning airplane under the control of a fully qualified and certificated crew is flown into terrain (or water or obstacles) with no apparent awareness on the part of the crew. Findings from these studies indicated that many such accidents could have been avoided if a warning device called a ground proximity warning system (“GPWS”) was used. Thereafter, advances in terrain mapping technology permitted vendors and designers of avionics equipment to develop newer type of GPWS that provides greater situational awareness for flight crews. The U.S. Federal Aviation Administration (“FAA”) has classified such systems as Terrain Awareness and Warning Systems (“TAWS”).
The advancement of technologies—more precise navigation systems, increased computer memory storage, and better display technology—have allowed further development of in the common features of TAWS: (1) use of airplane position information from the aircraft's navigation system(s), (2) an onboard terrain database, and (3) a means of displaying the surrounding terrain. Aircraft position information from the aircraft's navigation system is fed to a TAWS computer. The TAWS computer compares the airplane's current position and flight path with the terrain database associated with the system. If there is a potential threat of collision with terrain, the TAWS computer sends warning alerts to the airplane's audio system.
Regarding onboard terrain databases, various vendors and designers of avionics equipment have developed databases that have been, for all intents and purposes, proprietary in nature. Past and recent advances have made significant efforts to obtain digital elevation models of the Earth, generating a high-resolution digital topographical database. Governing authorities have been a primary source of gathering and compiling terrain elevation data into terrain databases on a large scale. For instance, the U.S. Geological Society (“USGS”) developed GTOPO30, a global digital elevation model (“DEM”). GTOPO30 terrain elevation data was derived from eight sources of data including Digital Terrain Elevation Data (“DTED”), Digital Chart of the World (“DCW”), USGS Digital Elevations Models (“DEM”), Army Map Services (“AMS”) Maps, International Map of the World (“IMW”), Peru Map, New Zealand DEM, and Antarctic Digital Database (“ADD”). The release of GTOPO30 represented the completion of global coverage of low-resolution elevation data; the resolution of GTOPO30 is generally thirty arc seconds (or approximately one kilometer). While the whole coverage of the terrain elevation data is positive, the low-resolution elevation data is not advantageous for a system such as TAWS because changes in terrain are reported at a one kilometer interval.
In February 2000, the Space Shuttle Endeavour acquired elevation data on a near-global scale during mission STS-99. In an international research effort known as Shuttle Radar Topography Mission (“SRTM”), a DEM was generated producing the most complete high-resolution digital topological database of Earth to date; the resolution is generally one arc second (or approximately 30 meters), thereby providing much greater detail than that provided with GTOPO30 data set. While the resolution of the terrain elevation data set is positive, there are three significant drawbacks of SRTM. First, the coverage extended from 56° South latitude to 60° North latitude only. Second, the SRTM terrain elevation data set is affected by mountainous and desert areas. Mountain summits of the Alpine and Andes ranges, and many gorges and canyons contain voids in the data. Third, at the present time, the resolution of one arc second is available over the United States territory only; the rest of the world is available at three arc seconds resolution.
The three-dimensional DEM data may also be categorized as a set of frequencies in two dimensions for the purposes of digital signal processing. One dimension may be North and the other may be East. Data characterized in this manner will have differences in frequency content. For example, GTOPO30 data set provides a very smooth surface with very few abrupt changes in elevations; it is low resolution, continuous, and virtually free of high-frequency noise. On the other hand, SRTM terrain elevation data set is high resolution and often contains high-frequency noise that may have been caused by radar artifacts of the Interferometric Synthetic Aperture Radar technique employed during the Shuttle mission to acquire the SRTM data.
Accordingly, each set of a plurality of terrain elevation data sets have advantages and disadvantages associated with it.